1. Field of the Invention
This invention relates to a laser driving apparatus, a laser driving method, an optical apparatus, an optical unit and a pulse current generation circuit, and more particularly to a correction technique for a load response waveform such as a laser emission light waveform.
2. Description of the Related Art
In an optical apparatus such as, for example, an optical disk apparatus or a light emitting apparatus which uses an optical cable or optical fiber, a system for pulse-driving a laser device is sometimes adopted. However, with this system, since the laser device is changed over at a high rate between light emission and no-light emission states, an overshoot, an undershoot, ringing, a response delay and so forth appear. Therefore, the system described is disadvantageous in that light emitted from the laser device does not exhibit a rectangular waveform.
Thus, a countermeasure for correcting, where a laser device is driven by pulses, the shape of the emission light waveform thereof so that driving current for the laser device may have a waveform as close as possible to a rectangular waveform has been proposed. Such a countermeasure as just described is disclosed, for example, in Japanese Patent Laid-Open No. 2005-340774 (hereinafter referred to as Patent Document 1) and Japanese Patent No. 4008748 (hereinafter referred to as Patent Document 2).
In Patent Document 1, a suppression current supplying circuit for supplying suppression current for moderating decrease of driving current after an overshoot which appears at a rising edge of driving current to be supplied from a driving current supplying circuit to a laser device is provided. The suppression current supplying circuit adds such current as to correct the shape of an emission light waveform and implements an appropriate shape of an emission light waveform by adjusting the timing and current value of the correction current. Patent Document 2 discloses a mechanism similar to that disclosed in Patent Document 1 but adapted to generate a timing signal, which defines a timing at which correction current is to be applied, based on a driving pulse.